1. Field of the Invention
This invention pertains to the field of polymer resins, curable thermoset resins, resin systems which include curable thermoset resins, composite materials and skin laminates for composite materials, and processes and intermediates for making the same.
2. Description of Related Art
Known gel coated fiber-reinforced polymers are subject to blistering if immersed in water or solvents for a prolonged period of time unless special measures are taken to prevent this phenomenon. Blisters are raised by localized swelling of the gel coated laminate due to diffusion of water into the composite and the presence of water-soluble constituents within the laminate. The blisters not only effect the external appearance of the gel coated fiber-reinforced polymer article, but also eventually lead to reduced composite strength.
Several methods have been proposed to reduce blistering in gel coated composite materials. U.S. Pat. No. 4,724,173 describes using a permeable gel coat to allow the osmotically active molecules to diffuse from the osmotic centers through the gel coat at a defined transport rate whereby the osmotic pressure of the osmotic centers is reduced so as to reduce blistering. U.S. Pat. No. 4,477,325 describes a method of manufacturing a skin barrier which has improved water resistance to protect the composite material from hydrolysis. U.S. Pat. Nos. 4,480,077 and 4,525,544 describe vinyl ester resin compositions which may be used in the laminate construction to impart greater resistance to water permeation and U.S. Pat. No. 4,959,259 describes a bisphenolic polyester resin composition which may also be used to impart greater water permeation resistance.
The latter technique, using a laminate resin having greater corrosion and/or water resistance, is the most common technique used by the composite industry to reduce blistering. Those resins are typically vinyl ester resins or isophthalic polyester resins. Not only is that technique not always completely successful, it also increases the overall expense of the composite material and/or reduces the flexibility in choosing the laminating resin for other desired properties.
For these and other reasons, further improvements in the ability to prevent blistering are desired. These improvements have special significance in outdoor and marine applications, bathtubs and shower stalls and environments exposed to chemicals, such as industrial and commercial applications. These and other objectives are achieved by the present invention.
One aspect of this invention is a process for making unsaturated polyetherester resins that are useful for making curable thermoset resin compositions comprising reacting at least one acid-terminated unsaturated polyetherester resin with at least one aromatic polyol having at least one non-primary hydroxy group to produce an unsaturated polyetherester resin at least partially end-capped with an aromatic polyol. The aromatic polyol end-capped unsaturated polyetherester resins obtainable by that process are also part of this invention.
Another aspect of this invention is curable thermoset resin compositions useful for imparting water and/or solvent resistance to gel coated fiber-reinforced polymers comprising:
(A) At least 5 wt. % of at least one aromatic polyol end-capped unsaturated polyetherester resin according to this invention;
(B) At least one unsaturated polyester resin having a number average molecular weight to the average number of double bonds per polymer molecule in the range from about 200 to about 400, in an amount such that the weight ratio of polyester resin (B) to polyetherester resin (A) is in the range from about 10:90 to about 90:10;
(C) About 10 to about 70 wt. % of at least one vinyl monomer; and
(D) At least one curing agent, and intermediates for making such curable thermoset resin compositions comprising all the components of the curable thermoset resin composition except the at least one curing agent (D).
Two more aspects of this invention are fiber-reinforced polymer composites obtainable by combining the curable thermoset resin composition according to this invention with reinforcing fiber and curing the curable thermoset resin composition and gel coated fiber-reinforced polymers comprising such fiber-reinforced compositions and a gel coat.
Yet another aspect of this invention is intermediates for making skin laminates for gel-coated fiber-reinforced composites, the intermediates comprising reinforcing fibers and the curable thermoset resin composition according to this invention in the form of a sheet.
A further aspect of this invention is gel coated polymer laminates comprising at least one fiber-reinforced polymer layer, at least one gel coat layer, and at least one thermoset resin layer interposed between the at least one fiber-reinforced polymer layer and the at least one gel coat layer, wherein the at least one thermoset resin layer is obtainable by applying the curable thermoset resin composition or the skin laminate intermediate according to this invention as a barrier layer between the gel coat layer and the fiber-reinforced polymer layer and curing the curable thermoset resin composition.
Two further aspects of this invention are methods for making a curable thermoset resin composition comprising combining:
(A) At least 5 wt. % of at least one unsaturated polyetherester resin according to this invention;
(B) At least one unsaturated polyester resin having a number average molecular weight to the average number of double bonds per polymer molecule in the range from about 200 to about 400, in an amount such that the weight ratio of polyester resin (B) to polyetherester resin (A) is in the range from about 10:90 to about 90:10;
(C) About 10 to about 70 wt. % of at least one vinyl monomer; and
(D) At least one curing agent.
Two further aspects of this invention are methods for reducing blistering of a gel coated fiber-reinforced polymer comprising:
(1) Applying at least one layer of the curable thermoset resin composition or the skin laminate intermediate of this invention between a gel coat layer and a fiber-reinforced polymer layer and
(2) Curing the curable thermoset resin composition, and articles obtainable by such methods.
The invention is described in further detail below.